Timing using Dasa alone is meaningless. In each of our breaths, all the planets are acting in tandem and even in Saturn Dasa, other planets will be co-acting as lords of antardasa, Paryanthardasas, Sookshmanthardasas and Dehanthardasas etc.
It will be foolish on the part of the Astrologer to say how your Saturn dasa will be for the long stretch of 19 years of its dasa. I think you should go for a detailed analysis.